DALLAS >> A criminal investigation is underway into an accidental poisoning involving a professional-grade pesticide that left four children dead and an Amarillo woman in critical condition, police said today.

Authorities are looking into why the family had the pesticide pellets, called Weevil-cide, which is only supposed to be sold to people with professional licenses or certification and is marketed for use in rodent control in commercial transport of commodities and animal feed.

The father told first responders through a Spanish language interpreter that he had spread the pellets under the family’s mobile home after obtaining the product from a friend, Amarillo Fire Capt. Larry Davis said. Davis said the product is not available for sale to the general public.

Davis said the father does not have that certification as far as he knows. He did not know whether the friend who gave him the product had a certification.

Amarillo police spokesman Officer Jeb Hilton says the department’s special crimes unit is investigating because of the child deaths. Once completed, the investigation will be turned over to the district attorney to determine whether charges will be filed. Hilton said other federal and state environmental regulation agencies may also investigate.

Fire officials said the children who died were three boys, ages 7, 9 and 11, and a 17-year-old girl. Officials have said all four children lived at the home in Amarillo, which is about 350 miles northwest of Dallas.

The children’s mother, Martha Balderas, 45, was in critical condition today at University Medical Center in Lubbock, according to a hospital spokesman. Five other family members, including the father and four other children, were being treated at BSA Health System in Amarillo and were in stable condition, hospital and fire officials said.

Crews who responded to a 5 a.m. call to the home on Monday originally thought it was related to carbon monoxide poisoning. Authorities later determined that phosphine gas was likely released when the father took a garden hose at some point Sunday and tried to rinse away some of the pellets because family members had complained of the smell.

The water started the chemical reaction that released the phosphine gas. A visitor arrived early Monday, found everyone sick and called 911.

Phosphine gas can cause respiratory failure and in severe cases can cause a pulmonary edema, which fills the lungs full of fluid.

About 10 first responders from the police, fire and medical response departments were also taken to the hospital as a precautionary measure, Davis said. Two were kept overnight for observation because of headache and nausea but were in good condition today, he said.

Chip Orton, emergency management coordinator for the city of Amarillo and Potter and Randall counties, says his staff was working with a number of state and federal agencies to decontaminate the home. The Texas Commission on Environmental Quality has hired a private contractor to help.

Orton said phosphine gas typically casts off in about eight to 12 hours after it’s been in contact with water, but emergency workers close to the home were wearing protective breathing equipment and hazmat suits as a precaution.

He said he does not know when the home will be safe for the family to return.